New cattle virus will help rule out BSE

A NEW virus that causes neurologic symptoms reminiscent of bovine spongiform encephalopathy (BSE) has been identified and its genome sequenced by a team of researchers that includes scientists at the University of California-Davis.

While this particular new virus is unlikely to pose a threat to human health or the food supply, the new findings are "critically important because they provide researchers with a relatively simple diagnostic tool that can reassure both ranchers and consumers" by ruling out BSE as the cause of neurologic symptoms when they appear in cattle, the announcement said.

Results of the study appear online in the September issue of the Emerging Infectious Diseases Journal, published by the U.S. Centers for Disease Control & Prevention.

"Neurologic disease in cattle can be difficult to diagnose because there are a number of different causes, and pre-mortem sampling and analyses can be cumbersome and/or expensive," said Patricia Pesavento, a veterinary pathologist in the University of California-Davis School of Veterinary Medicine and corresponding author on the paper.

"Understanding the role of this virus is crucial for veterinarians as well as for the dairy and beef cattle industries," she said. "Additionally, finding new viruses helps us identify other, more remote viruses because it builds our knowledge of both the depth and breadth of viral family trees."

In this new study, the researchers analyzed brain tissue from a yearling steer with neurologic symptoms of unknown cause. Through this analysis, they discovered a new virus that belongs to the astrovirus family. Further study of brain tissue samples preserved from earlier examinations of 32 cattle with unexplained neurologic symptoms revealed the presence of this astrovirus in three of those animals, the announcement said.

The researchers used "metagenomic" techniques to sequence this astrovirus species — now referred to as BoAstV0NeuroS. This newly identified virus becomes the third separate astrovirus species detected in brain tissues, and each is associated with neurologic disease.

Tissue analysis and distribution studies suggest that the cattle virus is most likely to be found in the spinal cord and causes a uniquely patterned tissue abnormality, thus enabling diagnosticians to quickly eliminate BSE as the cause of neurologic symptoms, the announcement said.

"Further research is needed to determine the viral origin and progression, like whether development of neurologic symptoms from this astrovirus requires other factors such as a co-infection by some other microbe or a weakened immune system," Pesavento said. "Further testing may also provide information about how often and for how long the animal sheds the virus."

Neurologic symptoms

Cattle that have neurologic symptoms are vigilantly screened to safeguard the human food chain from disease-causing microbes and toxins. These diseases — caused by bacteria, parasites, viruses, toxins or nutritional disturbances — include rabies, salmonella, listeria, chlamydia and BSE.

BSE has become a major public health concern after a connection was discovered between the disease in animals and a similar rare human ailment called variant Creutzfeldt-Jakob disease.

Early and rapid recognition of the causes of neurologic diseases in cattle is of the utmost importance; however, such a diagnosis is labor intensive, costly and challenging because of the large number of microbes and disorders that can cause neurologic diseases.

A wide variety of small astroviruses have been reported to infect mammals and birds, including humans, cattle, pigs, sheep, mink, dogs, cats, mice, sea lions, whales, chickens and turkeys.

People are frequently exposed to intestinal astroviruses, and infants, the elderly and individuals who have compromised immune systems are most at risk for experiencing acute symptoms of intestinal upset, the university explained.

Before this report, astroviruses had been implicated twice in neurologic disease: once in a teenage boy with a weakened immune system and also in an outbreak of "neurological shaking disease" in mink.